Watch your fonts. In an article for Writer's Digest, Ann Rittenberg asserts that faint type or small fonts are a common mistake that often lead to query rejection. If a busy editor or agent has to fight to read your letter, they'll often simply move on to the next in the pile. 12-point font is a nice standard.
Opt for simple white copy paper over fancy stationery. Colored or decorated paper is best left for notes to friends, rather than business correspondence.
Keep the photos at your desktop. An editor or agent will be investing in your words rather than your physical appearance. Don't distract from your best asset: your writing ability.
Follow submission instructions. Don't let a technicality stand in the way of your acceptance; if an editor or agent specifically requests an email query, do not contact that individual by mail.
Use the right envelope if an agent or editor prefers to be approached via mail. If that individual does not have specific instructions for packaging your query, place your letter in a 9 x 12 envelope, with a business-sized SASE included. Folding a business-sized SASE to fit inside another business-sized SASE can be awkward and cumbersome for a busy editor or agent -- ease of response increases your chance of receiving a response.
Consider your online life part of your submission package. If you provide links to a website or blog in your query, be sure to keep the content professional.
Remember that silly tactics carry an air of desperation. Oddball, attention-grabbing techniques cause an editor to question your own confidence in your work and wonder why you don't think your work is strong enough to sell itself. A query is a writer's resume; approach an editor or agent in the same professional manner that you would approach an interviewer when applying for a nine-to-five job.